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ABSTRACT

Organic-rich mudstones of the Appalachian Basin hold a sizable portion of the natural gas produced in the United States. Indeed, in 2015, Pennsylvania and West Virginia accounted for 21% of produced natural gas, driven in part by production from the Point Pleasant Limestone. The critical role that unconventional reservoirs will play in future global energy use necessitates the need for an enhanced understanding of those geological aspects that shape and influence their reservoir architecture. Foremost among these is a clearer understanding of the preservation and accumulation of organic carbon, as it is the source of hydrocarbons, and often provides the dominant host of interconnected porosity and hydrocarbon storage. To this end, pyrite morphology can offer insight into the redox conditions of the bottom and pore water environment at the time of sediment deposition and early diagenesis and can be especially useful in the analysis of deposits devoid of redox sensitive trace metals. Pyrite contained in cuttings and core chips retrieved from vertical and horizontal Point Pleasant Limestone wells were analyzed by scanning electron microscope. Results demonstrate a dearth of pyrite in the Point Pleasant (0.02–1.7% of the surface area analyzed). Pyrite morphology is dominated by euhedral grains and masses (~80% of pyrite encountered) co-occurring with infrequent framboids. Framboids are uniformly small (average = 4.7 μm) with just a few examples >10 μm. The presence of small amounts of euhedral pyrite grains and masses is consistent with accumulation under a dysoxic water column. Conversely, the size of the framboids suggests that they formed in a water column containing free hydrogen sulfide. A model invoking a lack of reactants necessary to sustain diagenetic pyrite growth in anoxic pore waters may explain this apparent paradox. In such a case, the framboid size distribution may reflect newly forming diagenetic framboids competing for a finite amount of reactants resulting in a population of small framboids and few large examples. Indeed, the low total iron/aluminum (Fe/Al) content of the Point Pleasant (average Fe/Al = 0.45) would indicate a low delivery of reactive iron to the seafloor during Point Pleasant deposition. The data suggests a model in which organic carbon preservation occurred by rapid burial and removal from oxygen-bearing water. In turn, more organic-rich and potentially higher quality reservoir facies of the Point Pleasant Limestone occur in areas of higher clastic delivery to basin.

INTRODUCTION

Recent years have witnessed a significant increase in hydrocarbon exploration of the Point Pleasant Limestone and Utica Shale Formations of the Appalachian Basin (Figure 1). Indeed, oil and natural gas production from these formations in Ohio constituted 45% and 58%, respectively, of the states total production in 2013 (Patchen and Carter, 2015). This production represents a significant increase from 2011, when these units accounted for just 1% of oil and 3.5% of natural gas produced (Patchen and Carter, 2015). Successful exploitation in Ohio in turn has led to increased exploration of the Point Pleasant and Utica in Pennsylvania and West Virginia. This burgeoning exploration necessitates an understanding of the environment in which these deposits accumulated and how that environment affected the generation and accumulation of hydrocarbons. Specifically, redox conditions of bottom and pore waters during deposition are of interest given the often-observed covariance of anoxia and organic carbon preservation in marine sediments (Demaison and Moore, 1980; Werne et al., 2002; Sageman et al., 2003). In this chapter, we assess the role of oxygen deprivation in the accumulation and diagenetic modification of marine sediments by use of redox-sensitive trace element concentrations and pyrite morphology.

Figure 1.

Stratigraphic chart depicting the subsurface nomenclature used in this study along with the surface nomenclature of Kentucky and Ohio. Adapted from McLaughlin et al. (2004) and Dattillo and Strunk (2016).

Figure 1.

Stratigraphic chart depicting the subsurface nomenclature used in this study along with the surface nomenclature of Kentucky and Ohio. Adapted from McLaughlin et al. (2004) and Dattillo and Strunk (2016).

Marine mudstones catalog a robust library of elemental data that can be used to deduce temporal variations in sediment supply, ocean hydrography, and redox conditions at the time of deposition and early diagenesis (Werne et al., 2002; Sageman et al., 2003; Brumsack, 2006; Tribovillard et al., 2006; Calvert and Pederson, 2007; Algeo and Tribovillard, 2009; Lash and Blood, 2014). Specifically, a suite of redox-sensitive trace elements, including molybdenum (Mo), uranium (U), vanadium (V), and chromium (Cr), is often used to determine the existence of bottom and pore water anoxia and euxinia in organic-rich mudstones (Sageman et al., 2003; Tribovillard et al., 2006; Rowe et al., 2008; Lash and Blood, 2014). However, in their chemostratigraphic investigation of the Upper Ordovician Trenton Limestone through Utica Shale (Figure 1) succession in a core from eastern New York State, Saboda and Lash (2014) demonstrate a paucity of redox-sensitive trace elements throughout the studied interval. Indeed, Saboda and Lash (2014) illustrate that U and Mo are present at levels only slightly enriched relative to crustal values, suggesting that widespread ocean anoxia may have sequestered the redox-sensitive trace element budget into deep ocean muds leaving behind water masses generally depleted in these trace metals (see Algeo, 2004). Given these observations, a robust relationship between redox-sensitive trace elements, redox conditions, and organic matter preservation is lacking in the Point Pleasant and Utica interval necessitating the need for an alternative assessment of redox conditions. This chapter seeks to understand organic matter preservation by investigating pyrite framboid diameters and redox-sensitive trace element data to determine the nature of bottom and pore water redox conditions during deposition and early diagenesis of the Point Pleasant Limestone in southwestern Pennsylvania and northern West Virginia (Figure 2).

Figure 2.

Location map depicting (A) the position of the Appalachian Basin during the Late Ordovician (Mohawkian), adapted and redrawn from Patchen et al. (2006), and (B) location of wells sampled in this study. Red circles indicate samples obtained from horizontal wellbores, whereas green circles indicate vertical wellbore data sets. Data points with half circles indicate both horizontal and vertical data sets on the same well.

Figure 2.

Location map depicting (A) the position of the Appalachian Basin during the Late Ordovician (Mohawkian), adapted and redrawn from Patchen et al. (2006), and (B) location of wells sampled in this study. Red circles indicate samples obtained from horizontal wellbores, whereas green circles indicate vertical wellbore data sets. Data points with half circles indicate both horizontal and vertical data sets on the same well.

STRATIGRAPHY AND GEOLOGIC SETTING

Orton (1873) assigned the name Point Pleasant to a series of beds exposed along the Ohio River near the town of Point Pleasant, Ohio, directly beneath the Kope Formation. Wickstrom et al.’s (1992) subsurface investigation of the Trenton Limestone and associated strata assigned the name Point Pleasant Formation to a succession of interbedded limestone and calcareous shale that grades vertically and laterally from the Trenton and underlies the Kope Formation in Ohio. Subsequent biostratigraphic and carbonate C-isotopic studies suggest that the Point Pleasant Formation of Wickstrom et al. (1992) is not correlative with the Point Pleasant of Orton (1873). Rather, the Point Pleasant of Wickstrom et al. (1992) is equivalent to the Upper Ordovician (Mohawkian) upper Grier Member through Devil’s Hollow Member of the Lexington Limestone Formation (Figure 1; Young et al., 2015; Dattilo and Strunk, 2016). Herein, we use the term Point Pleasant in effort to maintain consistency with previous subsurface investigations and petroleum geology considerations of this interval in Ohio (Cole et al., 1987; Wickstrom et al., 1992; Drozd and Cole, 1994).

Point Pleasant deposits accumulated in a southern subtropical subbasin defined by the Galena platform to the northwest, the Trenton platform to the northeast, and the Lexington platform to the southeast (Figure 2A; Scotese and McKerrow, 1990; Young et al., 2015). The narrow Sebree Trough connected the basin to the Iapetus Ocean to the southwest (Figure 2A; Kolata et al., 2001; Patchen et al., 2006; Patchen and Carter, 2015). In the study area (Figure 2B), the Point Pleasant comprises ~125 ft (38.1 m) of medium to dark gray organic-rich (maximum total organic carbon (TOC) = 4.5%) mudstone and interbedded limestone shell beds. The Point Pleasant Limestone was deposited in association with the drowning of the Ordovician carbonate platforms as a series of alternating mudstone and carbonate layers (McLaughlin et al., 2004). Siliciclastic deposits of the overlying Kope/Utica Formation represent the initial deposition of mudstone, siltstone, and sandstone comprising the Queenston clastic wedge (Ettenshon, 2004).

BACKGROUND

Pyrite Framboids and Use as Redox Indicators

Pyrite framboid size distribution provides a reliable measure of the paleo-redox conditions under which ancient marine deposits accumulated (Table 1; Wilkin et al., 1996; Wignall and Newton, 1998). Framboids, spherical aggregates of microcrystallites, form at or just below the sulfide chemocline, the boundary separating sulfide-bearing water from overlying oxygenated water. Here, ferrous iron species, sulfide species, and suitable electron receptors such as oxygen are available in enough quantity to promote the precipitation of iron-monosulfide (FeS) minerals such as mackinewite and greigite (Sweeney and Kaplan, 1973; Wilken and Barnes, 1997). The magnetic properties of greigite result in the rapidly forming microcrystallites attracting to one another to form spherical aggregates. Upon passing out of the zone of Fe reduction, FeS reacts rapidly with hydrogen sulfide (H2S) to form pyrite (Wilkin and Barnes, 1997). Associated euhedral pyrite crystals form more slowly and at saturation levels less than that necessary for the formation of diagenetic framboids. If bottom water is sulfidic, syngenetic framboids may form within the water column immediately beneath the sulfide chemocline (Wilkin et al., 1996, 1997). In this case, however, the dense framboids are unable to achieve diameters much in excess of 3–6 μm before their sinking away from the chemocline terminates their growth (Wilkin et al., 1996). A well-sorted population of very small framboids accumulates under these conditions. Conversely, when the chemocline resides at the sediment–water interface or within the sediment, the availability of reactants limits framboid growth. These sediments are characterized by a rather poorly sorted population of large (>10 μm) framboids (Wilkin et al., 1996). The presence of metabolizable organic matter for bacteria to reduce sulfate to sulfide, and reactive detrital iron minerals are the primary limiting factors of sedimentary pyrite formation (Berner, 1970, 1983).

Table 1.

Framboid size criteria used to define redox conditions (Bond and Wignall, 2010).

ConditionsFramboid Diameters and Associated Data
Euxinic (persistently sulfidic bottom water)Abundant small (mean diameter = 3–5 μm) framboids; narrow size range; few if any euhedral pyrite crystals
Anoxic (no oxygen in bottom water for extended periods of time)abundant small (mean diameter = 4–6 μm) framboids, including a small number of larger framboids; few euhedral pyrite crystals
Lower dysoxic (weakly oxygenated bottom water)Framboids 6–10 μm in diameter are moderately common; subordinate larger framboids and euhedral pyrite crystals
Upper dysoxic (partial oxygen restriction in bottom water)Large framboids are common; rare small (<5 μm diameter) framboids; most pyrite is euhedral crystalline
Oxic (on oxygen restriction)No framboids; rare pyrite crystals
ConditionsFramboid Diameters and Associated Data
Euxinic (persistently sulfidic bottom water)Abundant small (mean diameter = 3–5 μm) framboids; narrow size range; few if any euhedral pyrite crystals
Anoxic (no oxygen in bottom water for extended periods of time)abundant small (mean diameter = 4–6 μm) framboids, including a small number of larger framboids; few euhedral pyrite crystals
Lower dysoxic (weakly oxygenated bottom water)Framboids 6–10 μm in diameter are moderately common; subordinate larger framboids and euhedral pyrite crystals
Upper dysoxic (partial oxygen restriction in bottom water)Large framboids are common; rare small (<5 μm diameter) framboids; most pyrite is euhedral crystalline
Oxic (on oxygen restriction)No framboids; rare pyrite crystals

Framboid diameter analysis can be especially useful to the differentiation of deposits that accumulated under euxinic conditions from those of more oxygenated settings, especially dysoxic conditions defined by weakly oxygenated bottom water and variable levels of Fe reactivity (Table 1; Wilkin et al., 1996). However, it is noteworthy that the distinction between euxinic and suboxic bottom water is potentially less clear-cut if framboids are growing under reactant-limited conditions. For example, the abundance of small framboids (diameter = ~4 μm) in modern sediments of the Santa Barbara Basin that accumulated under a dysoxic water column has been attributed to a paucity of reactive Fe (Schieber and Schimmelmann, 2007). Morse and Wang (1996) have suggested that anoxic and euxinic environments promote high nucleation density of pyrite. Under these circumstances, framboids precipitating at multiple sites in anoxic pore water consume the limited supply of reactants resulting in a population of small diagenetic framboids. In some instances, these framboids approach the size distribution typical of those forming in a euxinic water column (Schieber and Schimmelmann, 2007).

Geochemical Proxies

Some portion of most marine sediment is of a detrital provenance, including eolian and fluvial inputs (Calvert and Pedersen, 2007). Aluminum is considered the principal conservative proxy for clay mineral flux in fine-grained clastic deposits (Arthur et al., 1985; Arthur and Dean, 1991; Calvert and Pedersen, 2007). Changes in grain size of the detrital flux can be recognized by consideration of variations in the relative abundances of those elements associated with the coarser size fraction relative to Al, including Ti and Zr (Sageman and Lyons, 2003). Further, the conservative behavior of Al in soil formation and weathering profiles favors its use as a parameter to assess authigenic enrichment of redox sensitive elements via Al normalization (Brumsack, 1989; Arthur et al., 1990).

Molybdenum and U are especially useful to paleoenvironmental analysis of modern and ancient oxygen-deficient marine systems for several reasons. First, detrital concentrations of both elements are low, U ~2.7 ppm and Mo ~3.7 ppm (Taylor and McLennan, 1985). Moreover, both elements have long residence times in seawater (~450 ka for U and ~780 ka for Mo) meaning that Mo and U exhibit nearly uniform global seawater concentrations (Algeo and Tribovillard, 2009). Finally, inasmuch as both elements are present in low concentrations in marine plankton, authigenic uptake from seawater enhanced by oxygen-deficient conditions leads to an enrichment of Mo and U in marine deposits (Algeo and Tribovillard, 2009).

The Fe/Al ratio has been used to aid in the recognition of water column (syngenetic) pyrite formation and, therefore, euxinic bottom water conditions (Lyons et al., 2003; Lyons and Kashgarian, 2005; Lyons and Severmann, 2006). The shuttling of dissolved Fe2+ as Fe-oxyhydroxide particulates from where the chemocline (the boundary separating oxygenated water from underlying oxygen-deficient water) impinges the seafloor enhances enrichment of bottom water in the reactive Fe necessary for the formation of syngenetic pyrite. The transported Fe2+ may then be sequestered in sulfidic bottom water by precipitation of sulfide minerals, including pyrite (Canfield et al., 1996; Lyons and Kashgarian, 2005; Raiswell and Anderson, 2005; Lyons and Severmann, 2006). This process gives rise to sediment represented by elevated Fe/Al (Lyons and Severmann, 2006) in excess of average shale values (Fe/Al = 0.55, Wedepohl, 1971; Fe/Al = 0.5, Taylor and McLennan, 1985).

METHODS

Pyrite and Framboid Diameter Analysis

Sixty-two Point Pleasant Limestone samples were selected for pyrite morphology analysis. The data set includes samples obtained by EQT Production from a core in Greene County, Pennsylvania, and drill cutting chips collected from three vertical and four horizontal exploration wells drilled in Greene County, Pennsylvania, and Wetzel County, West Virginia (Figure 2B, Table 2). Data sets from vertical well cores and cuttings provide an assessment of elemental data and pyrite morphology over the Point Pleasant stratigraphic interval, whereas horizontal well data sets provide insight into spatial changes along the path of the wellbore within a restricted stratigraphic interval. Measured depth (MD) denotes the position of a sample obtained from vertical wellbores. Sample position above the Trenton–Point Pleasant contact denotes the stratigraphic position of horizontal wellbore samples.

Table 2.

Framboid size data, pyrite occurrence, and geochemical data for Point Pleasant Limestone samples.

Sample LocationFramboid DataElemental Data
WellOrientationLocationDepthDistance above Trenton TopnMaximum DiameterMean DiameterStandard Deviaiton25th Percentile75th PercentileFramboid DensityBulk Rock PyriteFramboidal pyriteAlMo EFU EFFe/Al
   ftft μmμmμmμmμmframboids/mm2%%%   
Well AHorizontalGreeneaverage64.2109134.51.73.55.2140.7627.013.540.790.460.49
Well AHorizontalGreene13,67052.610993.91.634.7230.5635.46n/an/an/an/a
Well AHorizontalGreene14,54059.711493.91.43.14.6180.5633.89n/an/an/an/a
Well AHorizontalGreene15,59068.0116185.32.04.06.0100.5330.11n/an/an/an/a
Well AHorizontalGreene16,46076.495155.01.74.05.651.378.56n/an/an/an/a
Well BHorizontalGreeneaverage67.5127135.31.74.15.890.1223.542.982.900.100.47
Well BHorizontalGreene14,39076.1150196.12.34.86.790.094.79n/an/an/an/a
Well BHorizontalGreene15,02064.5170135.31.64.25.890.0266.28n/an/an/an/a
Well BHorizontalGreene16,01056.358135.41.84.05.920.196.96n/an/an/an/a
Well BHorizontalGreene17,00070.012874.21.23.34.9160.1816.13n/an/an/an/a
Well BHorizontalGreene17,99069.4126165.02.13.65.8110.0916.60n/an/an/an/a
Well BHorizontalGreene19,07068.662115.41.64.26.340.277.22n/an/an/an/a
Well CHorizontalWetzelaverage76.4146194.82.13.65.3270.4612.554.492.551.020.48
Well CHorizontalWetzel14,28081.1102103.81.52.74.7190.6419.25n/an/an/an/a
Well CHorizontalWetzel15,03073.6210404.93.23.85.2530.449.34n/an/an/an/a
Well CHorizontalWetzel15,99074.2160175.62.44.06.2100.333.98n/an/an/an/a
Well CHorizontalWetzel17,01072.6110104.71.43.85.2280.4417.63n/an/an/an/a
Well CHorizontalWetzel18,00078.2497113.81.42.84.51241.7323.09n/an/an/an/a
Well CHorizontalWetzel18,99078.4436124.01.52.94.71090.8633.05n/an/an/an/a
Well CVerticalWetzelaveragen/a103155.02.23.65.821n/an/a4.041.450.860.45
Well CVerticalWetzel13,030n/a108114.81.73.65.835n/an/an/an/an/an/a
Well CVerticalWetzel13,045n/a114265.83.43.86.423n/an/an/an/an/an/a
Well CVerticalWetzel13,055n/a106114.91.83.65.716n/an/an/an/an/an/a
Well CVerticalWetzel13,065n/a84124.71.83.55.212n/an/an/an/an/an/a
Well CVerticalWetzel13,075n/a106114.71.53.85.562n/an/an/an/an/an/a
Well CVerticalWetzel13,085n/a63145.92.54.06.99n/an/an/an/an/an/a
Well CVerticalWetzel13,100n/a101115.12.03.76.118n/an/an/an/an/an/a
Well CVerticalWetzel13,115n/a1395.41.54.36.32n/an/an/an/an/an/a
Well CVerticalWetzel13,130n/a3108.12.77.09.6< 1n/an/an/an/an/an/a
Well DHorizontalGreeneaverage76.410294.51.53.45.012n/an/a4.492.551.020.48
Well DHorizontalGreene13,88052.3102105.01.73.75.77n/an/an/an/an/an/a
Well DHorizontalGreene14,87066.110084.21.33.34.86n/an/an/an/an/an/a
Well DHorizontalGreene15,95080.5103114.81.63.75.311n/an/an/an/an/an/a
Well DHorizontalGreene16,94092.510373.81.22.94.325n/an/an/an/an/an/a
Well DHorizontalGreene17,93074.312784.01.23.14.756n/an/an/an/an/an/a
Well DHorizontalGreene18,85079.1100124.01.62.94.766n/an/an/an/an/an/a
Well DHorizontalGreene19,93079.310593.81.43.04.393n/an/an/an/an/an/a
Well DHorizontalGreene20,73087.0100104.71.83.45.613n/an/an/an/an/an/a
Well DVerticalGreeneaveragen/a84104.41.63.35.115n/an/a3.300.820.000.42
Well DVerticalGreene13,475n/a102105.01.63.85.919n/an/an/an/an/an/a
Well DVerticalGreene13,485n/a10383.81.42.84.57n/an/an/an/an/an/a
Well DVerticalGreene13,495n/a100144.31.93.14.828n/an/an/an/an/an/a
Well DVerticalGreene13,505n/a3084.31.43.55.07n/an/an/an/an/an/a
Well DVerticalGreene13,515n/a101124.21.63.15.035n/an/an/an/an/an/a
Well DVerticalGreene13,520n/a65114.41.43.64.97n/an/an/an/an/an/a
Well DVerticalGreene13,535n/a100114.61.73.25.416n/an/an/an/an/an/a
Well DVerticalGreene13,545n/a100145.02.13.55.711n/an/an/an/an/an/a
Well DVerticalGreene13,555n/a100134.01.82.74.632n/an/an/an/an/an/a
Well DVerticalGreene13,565n/a6994.11.53.24.95n/an/an/an/an/an/a
Well DVerticalGreene13,575n/a101144.31.93.45.220n/an/an/an/an/an/a
Well DVerticalGreene13,585n/a100113.92.22.25.110n/an/an/an/an/an/a
Well EVerticalGreeneaveragen/a80125.61.94.56.226n/an/a3.610.800.140.59
Well EVerticalGreene13,402.3n/a100115.71.74.66.522n/an/an/an/an/an/a
Well EVerticalGreene13,417.1n/a19165.92.94.45.93n/an/an/an/an/an/a
Well EVerticalGreene13,433.3n/a101115.01.54.15.334n/an/an/an/an/an/a
Well EVerticalGreene13,447.2n/a100115.81.54.87.023n/an/an/an/an/an/a
Well EVerticalGreene13,453.8n/a102116.31.94.97.737n/an/an/an/an/an/a
Well EVerticalGreene13,457.2n/a10184.41.23.55.135n/an/an/an/an/an/a
Well EVerticalGreene13,462.3n/a101124.91.43.95.632n/an/an/an/an/an/a
Well EVerticalGreene13,488.4n/a10094.51.43.45.324n/an/an/an/an/an/a
Well EVerticalGreene13,508.5n/a10094.61.53.55.320n/an/an/an/an/an/a
Well FVerticalWetzelaveragen/a29136.92.35.38.14n/an/a6.460.310.180.54
Well FVerticalWetzel12,240n/a29146.72.45.17.84n/an/an/an/an/an/a
Well FVerticalWetzel12,250n/a28179.23.36.711.14n/an/an/an/an/an/a
Well FVerticalWetzel12,260n/a41135.42.14.26.06n/an/an/an/an/an/a
Well FVerticalWetzel12,270n/a1696.41.65.17.52n/an/an/an/an/an/a
Well FVerticalWetzel12,280n/a19145.12.44.15.73n/an/an/an/an/an/a
Well FVerticalWetzel12,310n/a564.41.54.05.11n/an/an/an/an/an/a
Well FVerticalWetzel12,330n/a874.71.54.15.41n/an/an/an/an/an/a
Sample LocationFramboid DataElemental Data
WellOrientationLocationDepthDistance above Trenton TopnMaximum DiameterMean DiameterStandard Deviaiton25th Percentile75th PercentileFramboid DensityBulk Rock PyriteFramboidal pyriteAlMo EFU EFFe/Al
   ftft μmμmμmμmμmframboids/mm2%%%   
Well AHorizontalGreeneaverage64.2109134.51.73.55.2140.7627.013.540.790.460.49
Well AHorizontalGreene13,67052.610993.91.634.7230.5635.46n/an/an/an/a
Well AHorizontalGreene14,54059.711493.91.43.14.6180.5633.89n/an/an/an/a
Well AHorizontalGreene15,59068.0116185.32.04.06.0100.5330.11n/an/an/an/a
Well AHorizontalGreene16,46076.495155.01.74.05.651.378.56n/an/an/an/a
Well BHorizontalGreeneaverage67.5127135.31.74.15.890.1223.542.982.900.100.47
Well BHorizontalGreene14,39076.1150196.12.34.86.790.094.79n/an/an/an/a
Well BHorizontalGreene15,02064.5170135.31.64.25.890.0266.28n/an/an/an/a
Well BHorizontalGreene16,01056.358135.41.84.05.920.196.96n/an/an/an/a
Well BHorizontalGreene17,00070.012874.21.23.34.9160.1816.13n/an/an/an/a
Well BHorizontalGreene17,99069.4126165.02.13.65.8110.0916.60n/an/an/an/a
Well BHorizontalGreene19,07068.662115.41.64.26.340.277.22n/an/an/an/a
Well CHorizontalWetzelaverage76.4146194.82.13.65.3270.4612.554.492.551.020.48
Well CHorizontalWetzel14,28081.1102103.81.52.74.7190.6419.25n/an/an/an/a
Well CHorizontalWetzel15,03073.6210404.93.23.85.2530.449.34n/an/an/an/a
Well CHorizontalWetzel15,99074.2160175.62.44.06.2100.333.98n/an/an/an/a
Well CHorizontalWetzel17,01072.6110104.71.43.85.2280.4417.63n/an/an/an/a
Well CHorizontalWetzel18,00078.2497113.81.42.84.51241.7323.09n/an/an/an/a
Well CHorizontalWetzel18,99078.4436124.01.52.94.71090.8633.05n/an/an/an/a
Well CVerticalWetzelaveragen/a103155.02.23.65.821n/an/a4.041.450.860.45
Well CVerticalWetzel13,030n/a108114.81.73.65.835n/an/an/an/an/an/a
Well CVerticalWetzel13,045n/a114265.83.43.86.423n/an/an/an/an/an/a
Well CVerticalWetzel13,055n/a106114.91.83.65.716n/an/an/an/an/an/a
Well CVerticalWetzel13,065n/a84124.71.83.55.212n/an/an/an/an/an/a
Well CVerticalWetzel13,075n/a106114.71.53.85.562n/an/an/an/an/an/a
Well CVerticalWetzel13,085n/a63145.92.54.06.99n/an/an/an/an/an/a
Well CVerticalWetzel13,100n/a101115.12.03.76.118n/an/an/an/an/an/a
Well CVerticalWetzel13,115n/a1395.41.54.36.32n/an/an/an/an/an/a
Well CVerticalWetzel13,130n/a3108.12.77.09.6< 1n/an/an/an/an/an/a
Well DHorizontalGreeneaverage76.410294.51.53.45.012n/an/a4.492.551.020.48
Well DHorizontalGreene13,88052.3102105.01.73.75.77n/an/an/an/an/an/a
Well DHorizontalGreene14,87066.110084.21.33.34.86n/an/an/an/an/an/a
Well DHorizontalGreene15,95080.5103114.81.63.75.311n/an/an/an/an/an/a
Well DHorizontalGreene16,94092.510373.81.22.94.325n/an/an/an/an/an/a
Well DHorizontalGreene17,93074.312784.01.23.14.756n/an/an/an/an/an/a
Well DHorizontalGreene18,85079.1100124.01.62.94.766n/an/an/an/an/an/a
Well DHorizontalGreene19,93079.310593.81.43.04.393n/an/an/an/an/an/a
Well DHorizontalGreene20,73087.0100104.71.83.45.613n/an/an/an/an/an/a
Well DVerticalGreeneaveragen/a84104.41.63.35.115n/an/a3.300.820.000.42
Well DVerticalGreene13,475n/a102105.01.63.85.919n/an/an/an/an/an/a
Well DVerticalGreene13,485n/a10383.81.42.84.57n/an/an/an/an/an/a
Well DVerticalGreene13,495n/a100144.31.93.14.828n/an/an/an/an/an/a
Well DVerticalGreene13,505n/a3084.31.43.55.07n/an/an/an/an/an/a
Well DVerticalGreene13,515n/a101124.21.63.15.035n/an/an/an/an/an/a
Well DVerticalGreene13,520n/a65114.41.43.64.97n/an/an/an/an/an/a
Well DVerticalGreene13,535n/a100114.61.73.25.416n/an/an/an/an/an/a
Well DVerticalGreene13,545n/a100145.02.13.55.711n/an/an/an/an/an/a
Well DVerticalGreene13,555n/a100134.01.82.74.632n/an/an/an/an/an/a
Well DVerticalGreene13,565n/a6994.11.53.24.95n/an/an/an/an/an/a
Well DVerticalGreene13,575n/a101144.31.93.45.220n/an/an/an/an/an/a
Well DVerticalGreene13,585n/a100113.92.22.25.110n/an/an/an/an/an/a
Well EVerticalGreeneaveragen/a80125.61.94.56.226n/an/a3.610.800.140.59
Well EVerticalGreene13,402.3n/a100115.71.74.66.522n/an/an/an/an/an/a
Well EVerticalGreene13,417.1n/a19165.92.94.45.93n/an/an/an/an/an/a
Well EVerticalGreene13,433.3n/a101115.01.54.15.334n/an/an/an/an/an/a
Well EVerticalGreene13,447.2n/a100115.81.54.87.023n/an/an/an/an/an/a
Well EVerticalGreene13,453.8n/a102116.31.94.97.737n/an/an/an/an/an/a
Well EVerticalGreene13,457.2n/a10184.41.23.55.135n/an/an/an/an/an/a
Well EVerticalGreene13,462.3n/a101124.91.43.95.632n/an/an/an/an/an/a
Well EVerticalGreene13,488.4n/a10094.51.43.45.324n/an/an/an/an/an/a
Well EVerticalGreene13,508.5n/a10094.61.53.55.320n/an/an/an/an/an/a
Well FVerticalWetzelaveragen/a29136.92.35.38.14n/an/a6.460.310.180.54
Well FVerticalWetzel12,240n/a29146.72.45.17.84n/an/an/an/an/an/a
Well FVerticalWetzel12,250n/a28179.23.36.711.14n/an/an/an/an/an/a
Well FVerticalWetzel12,260n/a41135.42.14.26.06n/an/an/an/an/an/a
Well FVerticalWetzel12,270n/a1696.41.65.17.52n/an/an/an/an/an/a
Well FVerticalWetzel12,280n/a19145.12.44.15.73n/an/an/an/an/an/a
Well FVerticalWetzel12,310n/a564.41.54.05.11n/an/an/an/an/an/a
Well FVerticalWetzel12,330n/a874.71.54.15.41n/an/an/an/an/an/a

As a result of the brittleness of the samples used in this analysis, samples were cut to size and epoxy vacuum impregnated with a resin sensitive to high pressures and capable of maintaining the structural integrity of the sample. Samples were ground with silicon carbide paper at increasingly finer grits and finished with a series of diamond paste compounds. The prepared samples were examined using a Tescan MIRA3 XM field-emission scanning electron microscope (FE-SEM). Imaging was performed with backscattered electrons to illustrate any elemental differences that may be present and to distinguish high atomic density pyrite from the low atomic density matrix. For each sample, a high-resolution, large-area image survey was collected. Here, 2.042 mm2 areas were mapped with a 0.0733 μm pixel resolution via the collection of 100 images in a 10 × 10 grid. Bulk pyrite was quantified as the ratio of pixels of pyrite to pixels of the entire image. Individual images were examined by use of the IntelliSEM™ software package that permitted the identification, counting, and classification of framboids as “normal” or “welded.” “Welded” or “infilled” refers to framboids displaying evidence of secondary diagenetic pyrite growth that can infill interstitial spaces among microcrystallites, and/or partially to completely overgrown framboids (Figure 3; Wilken et al., 1996; Wilken and Barnes, 1997). Care was taken to measure framboids that lack evidence of secondary diagenetic pyrite growth that could misrepresent the original size of the framboid. Finally, the maximum diameter was measured. Although apparent diameters of framboids tend to underestimate their true diameter, Wilken et al. (1996) demonstrated the possible error in measurements to be <10%. Where feasible, a minimum of 100 framboids from each sample were measured to obtain a statistically valid sample size (see Wilkin et al., 1996).

Figure 3.

Scanning electron micrograph depicting normal and welded framboids in the Point Pleasant.

Figure 3.

Scanning electron micrograph depicting normal and welded framboids in the Point Pleasant.

Inorganic Geochemical Analysis

Inorganic geochemical assessment of the samples was performed on approximately 5 g of drill bit cuttings and core chips that was homogenized into a powder and pressed to form 31-mm-diameter pellets. The pellets were analyzed using a tabletop Spectro XEPOS III energy-dispersive X-ray fluorescence (ED-XRF) using a 50-W end-window X-ray tube and a Peltier cooled Silicon Drift Detector. The cuttings were captured at intervals ranging from 5 ft (1.5 m) to 10 ft (3 m) MD along the vertical and 30 ft (9.1 m) in the lateral sections of the wellbore and at one-foot intervals along the core. Thirteen major elements and 20 trace elements were quantitatively measured. Data quality control was maintained using a set of well-characterized international geochemical reference materials (GRMs). These internationally accepted GRMs are chosen to matrix-match the values of the samples analyzed to make any correction required because of instrument performance or drifts. GRMs chosen for this study were United States Geological Survey (USGS) Green River Shale (SGR-1), USGS mica schist (SDC-1), National Institute of Standards and Technology (NIST) limestone (1D), and NIST dolomitic limestone (88b). These standards are of varied lithology and sufficient to make any elemental correction required for the different formations expected in the study.

Finally, we present elemental data as elemental abundance in wt. % or ppm, Al-normalized ratios, and enrichment factors (EF) where the element to Al ratio of the sample is normalized to the element to Al ratio of the average shale (Wedephol, 1971, 1991).

Organic Geochemical Analysis

For TOC analysis, approximately 0.10 g of ground material was treated with concentrated hydrochloric acid for a minimum of two hours to removed carbonates. The samples were placed in a LECO crucible and dried at 230°F (110°C) for a minimum of one hour. The dried sample was then analyzed with a LECO 600 Carbon Analyzer with detection limits to 0.01 wt. %.

RESULTS

Greene County, Pennsylvania

Pyrite Morphology

Samples from wells A and B horizontal well bores were analyzed for total and framboidal pyrite abundance and framboid diameter. Samples from wells E and D vertical pilot hole, and well D horizontal wellbore were analyzed for framboid diameter only. Results are presented in Table 2. The average bulk pyrite abundance in wells A and B is 0.39% (range 0.02–1.37%). The average diameter of the 3863 framboids measured is 4.7 μm with a standard deviation (STDV) of 1.7 μm (Figure 4). The average maximum framboid diameter is 11.2 μm and framboid density is 21 framboids/mm2. Finally, 23% (range 5–66%) of pyrite occurs as framboidal pyrite in wells A and B lateral samples. Average framboid diameters show minimal change throughout the Point Pleasant stratigraphic interval (Figure 5A), not along the wellbore (Figure 5B).

Figure 4.

Plot of the mean vs. the standard deviation of framboids in the Point Pleasant.

Figure 4.

Plot of the mean vs. the standard deviation of framboids in the Point Pleasant.

Figure 5.

Framboid diameter data for well D with box and whisker plots depicting the mean and maximum framboid diameters demonstrating minimal variability in mean framboid size throughout (A) the stratigraphic section and (B) along the horizontal portion of the wellbore. Note that although minimal, larger framboids, represented by those >10 μm, do occur in some samples.

Figure 5.

Framboid diameter data for well D with box and whisker plots depicting the mean and maximum framboid diameters demonstrating minimal variability in mean framboid size throughout (A) the stratigraphic section and (B) along the horizontal portion of the wellbore. Note that although minimal, larger framboids, represented by those >10 μm, do occur in some samples.

Geochemistry

Three hundred and thirteen Point Pleasant samples from Greene County wells were analyzed for elemental abundance (Table 2). The average Al concentration is 3.6% (range 1.1–11.0%) or roughly 40% of the average shale value of 8.8% (Wedephol, 1971, 1991). There is a strong covariance between Fe and Al as depicted by well E (Figure 6; r2 = 0.95). The average Fe/Al for each well ranges from 0.40 to 0.49. The average Point Pleasant Fe/Al for the entire data set is 0.46. Molybdenum and U occurrence in the Point Pleasant is minimal. Indeed, of the 313 samples analyzed, only 67 contain measurable quantities of both Mo and U, approximately 20% of the sample population. Further, these samples exhibit modest enrichment in Mo and U, where EFs average 3.3 (range 0.3–7.7) and 1.4 (range 0.2–3.0), respectively.

Figure 6.

Plot of Al vs. Fe in well E. Note the strong covariance suggesting the strong role clastic influx plays in delivering Fe to the basin. The lack of a decoupling of Fe from Al also indicates minimal growth of authigenic pyrite.

Figure 6.

Plot of Al vs. Fe in well E. Note the strong covariance suggesting the strong role clastic influx plays in delivering Fe to the basin. The lack of a decoupling of Fe from Al also indicates minimal growth of authigenic pyrite.

Wetzel County, West Virginia

Pyrite Morphology

Samples recovered from well C lateral wellbore were analyzed for total and framboidal pyrite abundance and framboid diameter. Samples from wells C and F vertical pilot hole were analyzed for framboid diameters. Results are presented in Table 2. The average bulk pyrite in well C is 0.70% (range 0.33–1.73%). The average diameter of 2359 measured framboids is 5.4 μm with an STDV = 2.0 μm (Figure 4). The average maximum framboid diameter is 13.4 μm. Average framboid density is 25 framboids/mm2 and an average of 18% (range 4–33%) of the pyrite occurs as framboidal pyrite.

Geochemistry

One hundred and sixty Point Pleasant samples recovered from Wetzel county wells were analyzed for elemental abundance (Table 2). The Point Pleasant of Wetzel County displays slightly higher Al concentrations than Greene County at 4.6% (range 2.1–7.9%) whereas still approximately 50% depleted relative to the average shale (Wedephol, 1971, 1991). The average Fe/Al ratio for each well ranges from 0.45 to 0.48 (average = 0.47), a marginally higher Fe content than observed in Greene County. As with Greene County, the Wetzel County samples display a paucity of Mo and U. However, 67 samples demonstrate detectable levels of Mo and U, a 100% increase over that observed in Greene County. The average Mo EF of 4.1 (range and 1.1–29.3) and U EF of 3.0 (range 0.26–5.7) are slightly higher than that observed in Greene County.

DISCUSSION

The Point Pleasant Formation hosts a low concentration of pyrite (Figure 7A). Moreover, of the pyrite present, ~75 to 80% occurs as euhedral crystal masses and euhedral grains (Figure 7B). Oddly, the subordinate framboidal pyrite generally occurs as very small ~5 μm framboids (Figure 4B) with few examples >10 μm (Figure 4B). Although framboids are marginally larger in Wetzel County, framboid size varies little through the stratigraphic interval of the Point Pleasant (Figure 5A). Likewise, framboid size demonstrates little variation along a horizontal wellbore (Figure 5B). These observations suggest that the processes of pyrite and framboid formation remained largely consistent across the study area throughout Point Pleasant deposition.

Figure 7.

Scanning electron micrographs of the Point Pleasant Limestone depicting (A) the general scarcity of pyrite and (B) the occurrence of both euhedral (eu) small framboidal (sf, <6 μm) and large (lf, >10 μm) framboids.

Figure 7.

Scanning electron micrographs of the Point Pleasant Limestone depicting (A) the general scarcity of pyrite and (B) the occurrence of both euhedral (eu) small framboidal (sf, <6 μm) and large (lf, >10 μm) framboids.

The morphological occurrence of pyrite and the diameter of framboids in the Point Pleasant Limestone imply two opposing models for the position of the chemocline during pyrite formation. The prevalence of euhedral grains and a lack of framboidal pyrite (Table 2) suggest accumulation of sediments under a dysoxic to oxic water column; an interpretation consistent with the low occurrence of detectable Mo and U, and Fe/Al ratios at or below average shale values. However, the small diameter and narrow size range of analyzed framboids (Figure 5, Table 2) is suggestive of formation in suspension, inferring that the sulfide chemocline resided in the water column above anoxic-sulfidic (euxinic) bottom waters (Figure 4; Wilken et al., 1996).

An alternate explanation for the abundance of small framboids is a lack of those reactants necessary to the formation of pyrite (either reactive Fe or bacterially mediated H2S; cf. Wilken et al., 1996). The dominance of framboids displaying a mean diameter of ~2–4 μm forming under a dysoxic water column of the Santa Barbara Basin was attributed to a paucity of reactive Fe (Schieber and Schimmelmann, 2007). Here, anoxic-sulfidic conditions exist a few millimeters below the sediment–water interface. Reactive Fe mobilized from Fe-rich, terrigenous dominated winter sediment enters adjacent, Fe-poor, but organic-rich sediment deposited during summer. The rapid production of diagenetic framboids consumes the limited amount of Fe in the summer sediment resulting in a population of small framboids (Schieber and Schimmelmann, 2007).

Average Al concentrations of the Point Pleasant Limestone of Greene and Wetzel counties, 3.6% and 4.6%, respectively, are significantly less than the average shale value of 8.8% (Wedepohl, 1971, 1991). This indicates a significantly diminished clastic flux, including the requisite reactive iron for the production of diagenetic pyrite. Indeed, the covariance of Al and Fe observed in the Point Pleasant (Figure 7) illustrates the critical role the detrital load played in delivering Fe to the basin. Moreover, the strong covariance of framboids with Al (r2 = 0.74) would also suggest a relationship between clastic influx and framboid occurrence, where clastic delivery of reactive Fe enabled the production of framboids (Figure 8).

Figure 8.

Plot of Al vs. framboid density. A strong relationship exists between increased clastic influx, attendant influx of reactive Fe, and the number of framboids encountered in the samples. This suggests that the availability of reactive Fe delivered to the basin limits framboid growth.

Figure 8.

Plot of Al vs. framboid density. A strong relationship exists between increased clastic influx, attendant influx of reactive Fe, and the number of framboids encountered in the samples. This suggests that the availability of reactive Fe delivered to the basin limits framboid growth.

The small average diameter of Point Pleasant framboids and their narrow size distribution warrants further discussion. Morse and Wang (1996) postulate that generally narrow size range of diagenetic minerals reflects the supersaturation of pore fluids and consequent rapid formation of multiple nuclei. In turn, growth at nucleation points occurs at a roughly uniform rate until equilibrium is reached. Indeed, if all framboids in a volume of sediment initiated growth at the same time and grew at the same rate, the result would be a framboid population of one size (Wilken et al., 1996). However, a range in sizes of observed framboids, as is the case in the Point Pleasant, suggests framboids nucleated at different times (Wilken et al., 1996). Under such circumstances of continuous nucleation, however, framboids may still approach a uniform size given that (1) framboids are generally assumed to grow at a constant growth rate (Wilken et al., 1996) and (2) as saturation diminishes, nucleation ceases but growth continues, and therefore, the difference in grain size between framboids of different ages diminishes (Morse and Wang, 1996).

The simplest explanation for the small size of Point Pleasant framboids involves the ratio of nuclei vs. the supply of reactants. In this scenario, nucleating framboids competing for a finite amount of reactants exhaust the supply before framboids have an opportunity to achieve diameters typical of diagenetic framboids (>10 μm). A “sphere of influence” may also contribute to the small size of framboids (Mores and Wang, 1996). That is, diagenetic framboids competing for finite resources have a small area from which to pull the reactants before the supply is exhausted because of either minimal input of the reactant into the system or having to compete with nearby framboids. Thus, under such conditions, diagenetic framboids in the Point Pleasant would have exhausted the reservoir of reactive Fe before attaining the large sizes more typical of diagenetic framboids (>~10 μm). Again, it is worth noting that although framboids >10 μm are uncommon (~2% of the framboid population, Table 2), their presence in 44 of 62 analyzed samples points unambiguously to the growth of diagenetic framboids. In sum, we argue that the framboid population of the Point Pleasant reflects the formation of diagenetic framboids under an oxic to dysoxic water column wherein growth was limited by a lack of necessary reactants, namely reactive Fe. Such a model for framboid formation is consistent with the general scarcity of pyrite and prevalence of diagenetic euhedral grains (~75–80% of observed pyrite; Figure 7). Indeed, euhedral grains are readily observed in those sediments where less reactive Fe forms from direct interaction with free H2S in pore waters under a dysoxic water column (Wilken et al., 1996). Furthermore, U and Mo at or below average shale concentrations are consistent with a water column that rarely achieved the anoxic and/or euxinic conditions necessary for their enrichment in marine sediments (Algeo and Tribovillard, 2009).

CONCLUSIONS

The Point Pleasant Limestone hosts a pyrite population comprising euhedral grains and subordinate framboids. The consistently small framboids observed likely formed in a diagenetic environment deficient in reactive Fe, and do not imply the formation of syngenetic framboids suspended in a euxinic water column (cf. Wilken et al., 1996). Indeed, the strong covariance of Fe and Al and the low amount of Al in the Point Pleasant are consistent with such a model. Further, the low occurrence of pyrite and lack of detectable abundances of redox sensitive trace elements, notably U and Mo, are consistent with accumulation in a dysoxic to possibly oxic water column. Burial of organic matter and its removal from zones of oxidization likely contributed to its preservation in these deposits.

ACKNOWLEDGMENTS

We thank Wayne Camp and Neil Fishman for their invitation to contribute to this volume. We extend our gratitude to Gary Lash for the many fruitful discussions, guidance, and efforts to improve this chapter. This chapter benefited from the thorough review of two anonymous reviewers. Finally, we thank EQT Production for their permission to generate and use the data sets in this publication.

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Figures & Tables

Figure 1.

Stratigraphic chart depicting the subsurface nomenclature used in this study along with the surface nomenclature of Kentucky and Ohio. Adapted from McLaughlin et al. (2004) and Dattillo and Strunk (2016).

Figure 1.

Stratigraphic chart depicting the subsurface nomenclature used in this study along with the surface nomenclature of Kentucky and Ohio. Adapted from McLaughlin et al. (2004) and Dattillo and Strunk (2016).

Figure 2.

Location map depicting (A) the position of the Appalachian Basin during the Late Ordovician (Mohawkian), adapted and redrawn from Patchen et al. (2006), and (B) location of wells sampled in this study. Red circles indicate samples obtained from horizontal wellbores, whereas green circles indicate vertical wellbore data sets. Data points with half circles indicate both horizontal and vertical data sets on the same well.

Figure 2.

Location map depicting (A) the position of the Appalachian Basin during the Late Ordovician (Mohawkian), adapted and redrawn from Patchen et al. (2006), and (B) location of wells sampled in this study. Red circles indicate samples obtained from horizontal wellbores, whereas green circles indicate vertical wellbore data sets. Data points with half circles indicate both horizontal and vertical data sets on the same well.

Figure 3.

Scanning electron micrograph depicting normal and welded framboids in the Point Pleasant.

Figure 3.

Scanning electron micrograph depicting normal and welded framboids in the Point Pleasant.

Figure 4.

Plot of the mean vs. the standard deviation of framboids in the Point Pleasant.

Figure 4.

Plot of the mean vs. the standard deviation of framboids in the Point Pleasant.

Figure 5.

Framboid diameter data for well D with box and whisker plots depicting the mean and maximum framboid diameters demonstrating minimal variability in mean framboid size throughout (A) the stratigraphic section and (B) along the horizontal portion of the wellbore. Note that although minimal, larger framboids, represented by those >10 μm, do occur in some samples.

Figure 5.

Framboid diameter data for well D with box and whisker plots depicting the mean and maximum framboid diameters demonstrating minimal variability in mean framboid size throughout (A) the stratigraphic section and (B) along the horizontal portion of the wellbore. Note that although minimal, larger framboids, represented by those >10 μm, do occur in some samples.

Figure 6.

Plot of Al vs. Fe in well E. Note the strong covariance suggesting the strong role clastic influx plays in delivering Fe to the basin. The lack of a decoupling of Fe from Al also indicates minimal growth of authigenic pyrite.

Figure 6.

Plot of Al vs. Fe in well E. Note the strong covariance suggesting the strong role clastic influx plays in delivering Fe to the basin. The lack of a decoupling of Fe from Al also indicates minimal growth of authigenic pyrite.

Figure 7.

Scanning electron micrographs of the Point Pleasant Limestone depicting (A) the general scarcity of pyrite and (B) the occurrence of both euhedral (eu) small framboidal (sf, <6 μm) and large (lf, >10 μm) framboids.

Figure 7.

Scanning electron micrographs of the Point Pleasant Limestone depicting (A) the general scarcity of pyrite and (B) the occurrence of both euhedral (eu) small framboidal (sf, <6 μm) and large (lf, >10 μm) framboids.

Figure 8.

Plot of Al vs. framboid density. A strong relationship exists between increased clastic influx, attendant influx of reactive Fe, and the number of framboids encountered in the samples. This suggests that the availability of reactive Fe delivered to the basin limits framboid growth.

Figure 8.

Plot of Al vs. framboid density. A strong relationship exists between increased clastic influx, attendant influx of reactive Fe, and the number of framboids encountered in the samples. This suggests that the availability of reactive Fe delivered to the basin limits framboid growth.

Table 1.

Framboid size criteria used to define redox conditions (Bond and Wignall, 2010).

ConditionsFramboid Diameters and Associated Data
Euxinic (persistently sulfidic bottom water)Abundant small (mean diameter = 3–5 μm) framboids; narrow size range; few if any euhedral pyrite crystals
Anoxic (no oxygen in bottom water for extended periods of time)abundant small (mean diameter = 4–6 μm) framboids, including a small number of larger framboids; few euhedral pyrite crystals
Lower dysoxic (weakly oxygenated bottom water)Framboids 6–10 μm in diameter are moderately common; subordinate larger framboids and euhedral pyrite crystals
Upper dysoxic (partial oxygen restriction in bottom water)Large framboids are common; rare small (<5 μm diameter) framboids; most pyrite is euhedral crystalline
Oxic (on oxygen restriction)No framboids; rare pyrite crystals
ConditionsFramboid Diameters and Associated Data
Euxinic (persistently sulfidic bottom water)Abundant small (mean diameter = 3–5 μm) framboids; narrow size range; few if any euhedral pyrite crystals
Anoxic (no oxygen in bottom water for extended periods of time)abundant small (mean diameter = 4–6 μm) framboids, including a small number of larger framboids; few euhedral pyrite crystals
Lower dysoxic (weakly oxygenated bottom water)Framboids 6–10 μm in diameter are moderately common; subordinate larger framboids and euhedral pyrite crystals
Upper dysoxic (partial oxygen restriction in bottom water)Large framboids are common; rare small (<5 μm diameter) framboids; most pyrite is euhedral crystalline
Oxic (on oxygen restriction)No framboids; rare pyrite crystals
Table 2.

Framboid size data, pyrite occurrence, and geochemical data for Point Pleasant Limestone samples.

Sample LocationFramboid DataElemental Data
WellOrientationLocationDepthDistance above Trenton TopnMaximum DiameterMean DiameterStandard Deviaiton25th Percentile75th PercentileFramboid DensityBulk Rock PyriteFramboidal pyriteAlMo EFU EFFe/Al
   ftft μmμmμmμmμmframboids/mm2%%%   
Well AHorizontalGreeneaverage64.2109134.51.73.55.2140.7627.013.540.790.460.49
Well AHorizontalGreene13,67052.610993.91.634.7230.5635.46n/an/an/an/a
Well AHorizontalGreene14,54059.711493.91.43.14.6180.5633.89n/an/an/an/a
Well AHorizontalGreene15,59068.0116185.32.04.06.0100.5330.11n/an/an/an/a
Well AHorizontalGreene16,46076.495155.01.74.05.651.378.56n/an/an/an/a
Well BHorizontalGreeneaverage67.5127135.31.74.15.890.1223.542.982.900.100.47
Well BHorizontalGreene14,39076.1150196.12.34.86.790.094.79n/an/an/an/a
Well BHorizontalGreene15,02064.5170135.31.64.25.890.0266.28n/an/an/an/a
Well BHorizontalGreene16,01056.358135.41.84.05.920.196.96n/an/an/an/a
Well BHorizontalGreene17,00070.012874.21.23.34.9160.1816.13n/an/an/an/a
Well BHorizontalGreene17,99069.4126165.02.13.65.8110.0916.60n/an/an/an/a
Well BHorizontalGreene19,07068.662115.41.64.26.340.277.22n/an/an/an/a
Well CHorizontalWetzelaverage76.4146194.82.13.65.3270.4612.554.492.551.020.48
Well CHorizontalWetzel14,28081.1102103.81.52.74.7190.6419.25n/an/an/an/a
Well CHorizontalWetzel15,03073.6210404.93.23.85.2530.449.34n/an/an/an/a
Well CHorizontalWetzel15,99074.2160175.62.44.06.2100.333.98n/an/an/an/a
Well CHorizontalWetzel17,01072.6110104.71.43.85.2280.4417.63n/an/an/an/a
Well CHorizontalWetzel18,00078.2497113.81.42.84.51241.7323.09n/an/an/an/a
Well CHorizontalWetzel18,99078.4436124.01.52.94.71090.8633.05n/an/an/an/a
Well CVerticalWetzelaveragen/a103155.02.23.65.821n/an/a4.041.450.860.45
Well CVerticalWetzel13,030n/a108114.81.73.65.835n/an/an/an/an/an/a
Well CVerticalWetzel13,045n/a114265.83.43.86.423n/an/an/an/an/an/a
Well CVerticalWetzel13,055n/a106114.91.83.65.716n/an/an/an/an/an/a
Well CVerticalWetzel13,065n/a84124.71.83.55.212n/an/an/an/an/an/a
Well CVerticalWetzel13,075n/a106114.71.53.85.562n/an/an/an/an/an/a
Well CVerticalWetzel13,085n/a63145.92.54.06.99n/an/an/an/an/an/a
Well CVerticalWetzel13,100n/a101115.12.03.76.118n/an/an/an/an/an/a
Well CVerticalWetzel13,115n/a1395.41.54.36.32n/an/an/an/an/an/a
Well CVerticalWetzel13,130n/a3108.12.77.09.6< 1n/an/an/an/an/an/a
Well DHorizontalGreeneaverage76.410294.51.53.45.012n/an/a4.492.551.020.48
Well DHorizontalGreene13,88052.3102105.01.73.75.77n/an/an/an/an/an/a
Well DHorizontalGreene14,87066.110084.21.33.34.86n/an/an/an/an/an/a
Well DHorizontalGreene15,95080.5103114.81.63.75.311n/an/an/an/an/an/a
Well DHorizontalGreene16,94092.510373.81.22.94.325n/an/an/an/an/an/a
Well DHorizontalGreene17,93074.312784.01.23.14.756n/an/an/an/an/an/a
Well DHorizontalGreene18,85079.1100124.01.62.94.766n/an/an/an/an/an/a
Well DHorizontalGreene19,93079.310593.81.43.04.393n/an/an/an/an/an/a
Well DHorizontalGreene20,73087.0100104.71.83.45.613n/an/an/an/an/an/a
Well DVerticalGreeneaveragen/a84104.41.63.35.115n/an/a3.300.820.000.42
Well DVerticalGreene13,475n/a102105.01.63.85.919n/an/an/an/an/an/a
Well DVerticalGreene13,485n/a10383.81.42.84.57n/an/an/an/an/an/a
Well DVerticalGreene13,495n/a100144.31.93.14.828n/an/an/an/an/an/a
Well DVerticalGreene13,505n/a3084.31.43.55.07n/an/an/an/an/an/a
Well DVerticalGreene13,515n/a101124.21.63.15.035n/an/an/an/an/an/a
Well DVerticalGreene13,520n/a65114.41.43.64.97n/an/an/an/an/an/a
Well DVerticalGreene13,535n/a100114.61.73.25.416n/an/an/an/an/an/a
Well DVerticalGreene13,545n/a100145.02.13.55.711n/an/an/an/an/an/a
Well DVerticalGreene13,555n/a100134.01.82.74.632n/an/an/an/an/an/a
Well DVerticalGreene13,565n/a6994.11.53.24.95n/an/an/an/an/an/a
Well DVerticalGreene13,575n/a101144.31.93.45.220n/an/an/an/an/an/a
Well DVerticalGreene13,585n/a100113.92.22.25.110n/an/an/an/an/an/a
Well EVerticalGreeneaveragen/a80125.61.94.56.226n/an/a3.610.800.140.59
Well EVerticalGreene13,402.3n/a100115.71.74.66.522n/an/an/an/an/an/a
Well EVerticalGreene13,417.1n/a19165.92.94.45.93n/an/an/an/an/an/a
Well EVerticalGreene13,433.3n/a101115.01.54.15.334n/an/an/an/an/an/a
Well EVerticalGreene13,447.2n/a100115.81.54.87.023n/an/an/an/an/an/a
Well EVerticalGreene13,453.8n/a102116.31.94.97.737n/an/an/an/an/an/a
Well EVerticalGreene13,457.2n/a10184.41.23.55.135n/an/an/an/an/an/a
Well EVerticalGreene13,462.3n/a101124.91.43.95.632n/an/an/an/an/an/a
Well EVerticalGreene13,488.4n/a10094.51.43.45.324n/an/an/an/an/an/a
Well EVerticalGreene13,508.5n/a10094.61.53.55.320n/an/an/an/an/an/a
Well FVerticalWetzelaveragen/a29136.92.35.38.14n/an/a6.460.310.180.54
Well FVerticalWetzel12,240n/a29146.72.45.17.84n/an/an/an/an/an/a
Well FVerticalWetzel12,250n/a28179.23.36.711.14n/an/an/an/an/an/a
Well FVerticalWetzel12,260n/a41135.42.14.26.06n/an/an/an/an/an/a
Well FVerticalWetzel12,270n/a1696.41.65.17.52n/an/an/an/an/an/a
Well FVerticalWetzel12,280n/a19145.12.44.15.73n/an/an/an/an/an/a
Well FVerticalWetzel12,310n/a564.41.54.05.11n/an/an/an/an/an/a
Well FVerticalWetzel12,330n/a874.71.54.15.41n/an/an/an/an/an/a
Sample LocationFramboid DataElemental Data
WellOrientationLocationDepthDistance above Trenton TopnMaximum DiameterMean DiameterStandard Deviaiton25th Percentile75th PercentileFramboid DensityBulk Rock PyriteFramboidal pyriteAlMo EFU EFFe/Al
   ftft μmμmμmμmμmframboids/mm2%%%   
Well AHorizontalGreeneaverage64.2109134.51.73.55.2140.7627.013.540.790.460.49
Well AHorizontalGreene13,67052.610993.91.634.7230.5635.46n/an/an/an/a
Well AHorizontalGreene14,54059.711493.91.43.14.6180.5633.89n/an/an/an/a
Well AHorizontalGreene15,59068.0116185.32.04.06.0100.5330.11n/an/an/an/a
Well AHorizontalGreene16,46076.495155.01.74.05.651.378.56n/an/an/an/a
Well BHorizontalGreeneaverage67.5127135.31.74.15.890.1223.542.982.900.100.47
Well BHorizontalGreene14,39076.1150196.12.34.86.790.094.79n/an/an/an/a
Well BHorizontalGreene15,02064.5170135.31.64.25.890.0266.28n/an/an/an/a
Well BHorizontalGreene16,01056.358135.41.84.05.920.196.96n/an/an/an/a
Well BHorizontalGreene17,00070.012874.21.23.34.9160.1816.13n/an/an/an/a
Well BHorizontalGreene17,99069.4126165.02.13.65.8110.0916.60n/an/an/an/a
Well BHorizontalGreene19,07068.662115.41.64.26.340.277.22n/an/an/an/a
Well CHorizontalWetzelaverage76.4146194.82.13.65.3270.4612.554.492.551.020.48
Well CHorizontalWetzel14,28081.1102103.81.52.74.7190.6419.25n/an/an/an/a
Well CHorizontalWetzel15,03073.6210404.93.23.85.2530.449.34n/an/an/an/a
Well CHorizontalWetzel15,99074.2160175.62.44.06.2100.333.98n/an/an/an/a
Well CHorizontalWetzel17,01072.6110104.71.43.85.2280.4417.63n/an/an/an/a
Well CHorizontalWetzel18,00078.2497113.81.42.84.51241.7323.09n/an/an/an/a
Well CHorizontalWetzel18,99078.4436124.01.52.94.71090.8633.05n/an/an/an/a
Well CVerticalWetzelaveragen/a103155.02.23.65.821n/an/a4.041.450.860.45
Well CVerticalWetzel13,030n/a108114.81.73.65.835n/an/an/an/an/an/a
Well CVerticalWetzel13,045n/a114265.83.43.86.423n/an/an/an/an/an/a
Well CVerticalWetzel13,055n/a106114.91.83.65.716n/an/an/an/an/an/a
Well CVerticalWetzel13,065n/a84124.71.83.55.212n/an/an/an/an/an/a
Well CVerticalWetzel13,075n/a106114.71.53.85.562n/an/an/an/an/an/a
Well CVerticalWetzel13,085n/a63145.92.54.06.99n/an/an/an/an/an/a
Well CVerticalWetzel13,100n/a101115.12.03.76.118n/an/an/an/an/an/a
Well CVerticalWetzel13,115n/a1395.41.54.36.32n/an/an/an/an/an/a
Well CVerticalWetzel13,130n/a3108.12.77.09.6< 1n/an/an/an/an/an/a
Well DHorizontalGreeneaverage76.410294.51.53.45.012n/an/a4.492.551.020.48
Well DHorizontalGreene13,88052.3102105.01.73.75.77n/an/an/an/an/an/a
Well DHorizontalGreene14,87066.110084.21.33.34.86n/an/an/an/an/an/a
Well DHorizontalGreene15,95080.5103114.81.63.75.311n/an/an/an/an/an/a
Well DHorizontalGreene16,94092.510373.81.22.94.325n/an/an/an/an/an/a
Well DHorizontalGreene17,93074.312784.01.23.14.756n/an/an/an/an/an/a
Well DHorizontalGreene18,85079.1100124.01.62.94.766n/an/an/an/an/an/a
Well DHorizontalGreene19,93079.310593.81.43.04.393n/an/an/an/an/an/a
Well DHorizontalGreene20,73087.0100104.71.83.45.613n/an/an/an/an/an/a
Well DVerticalGreeneaveragen/a84104.41.63.35.115n/an/a3.300.820.000.42
Well DVerticalGreene13,475n/a102105.01.63.85.919n/an/an/an/an/an/a
Well DVerticalGreene13,485n/a10383.81.42.84.57n/an/an/an/an/an/a
Well DVerticalGreene13,495n/a100144.31.93.14.828n/an/an/an/an/an/a
Well DVerticalGreene13,505n/a3084.31.43.55.07n/an/an/an/an/an/a
Well DVerticalGreene13,515n/a101124.21.63.15.035n/an/an/an/an/an/a
Well DVerticalGreene13,520n/a65114.41.43.64.97n/an/an/an/an/an/a
Well DVerticalGreene13,535n/a100114.61.73.25.416n/an/an/an/an/an/a
Well DVerticalGreene13,545n/a100145.02.13.55.711n/an/an/an/an/an/a
Well DVerticalGreene13,555n/a100134.01.82.74.632n/an/an/an/an/an/a
Well DVerticalGreene13,565n/a6994.11.53.24.95n/an/an/an/an/an/a
Well DVerticalGreene13,575n/a101144.31.93.45.220n/an/an/an/an/an/a
Well DVerticalGreene13,585n/a100113.92.22.25.110n/an/an/an/an/an/a
Well EVerticalGreeneaveragen/a80125.61.94.56.226n/an/a3.610.800.140.59
Well EVerticalGreene13,402.3n/a100115.71.74.66.522n/an/an/an/an/an/a
Well EVerticalGreene13,417.1n/a19165.92.94.45.93n/an/an/an/an/an/a
Well EVerticalGreene13,433.3n/a101115.01.54.15.334n/an/an/an/an/an/a
Well EVerticalGreene13,447.2n/a100115.81.54.87.023n/an/an/an/an/an/a
Well EVerticalGreene13,453.8n/a102116.31.94.97.737n/an/an/an/an/an/a
Well EVerticalGreene13,457.2n/a10184.41.23.55.135n/an/an/an/an/an/a
Well EVerticalGreene13,462.3n/a101124.91.43.95.632n/an/an/an/an/an/a
Well EVerticalGreene13,488.4n/a10094.51.43.45.324n/an/an/an/an/an/a
Well EVerticalGreene13,508.5n/a10094.61.53.55.320n/an/an/an/an/an/a
Well FVerticalWetzelaveragen/a29136.92.35.38.14n/an/a6.460.310.180.54
Well FVerticalWetzel12,240n/a29146.72.45.17.84n/an/an/an/an/an/a
Well FVerticalWetzel12,250n/a28179.23.36.711.14n/an/an/an/an/an/a
Well FVerticalWetzel12,260n/a41135.42.14.26.06n/an/an/an/an/an/a
Well FVerticalWetzel12,270n/a1696.41.65.17.52n/an/an/an/an/an/a
Well FVerticalWetzel12,280n/a19145.12.44.15.73n/an/an/an/an/an/a
Well FVerticalWetzel12,310n/a564.41.54.05.11n/an/an/an/an/an/a
Well FVerticalWetzel12,330n/a874.71.54.15.41n/an/an/an/an/an/a

Contents

GeoRef

References

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